1. Field of the Invention
The present invention relates generally to control systems for vehicle engines, and more particularly, to a system for controlling an engine output adjusting device provided in a vehicle engine, such as a throttle valve, through an electric actuator provided for driving the engine output adjusting device in accordance with a controlled change in the position of an accelerator pedal accompanied with the vehicle engine.
2. Description of the Prior Art
It is well known, in a vehicle engine, to use a throttle valve which is controlled to vary its opening degree in accordance with a controlled change in the position of an accelerator pedal accompanied with the vehicle engine by way of a mechanical linkage provided between the accelerator and the throttle valve. A throttle valve control system for electrically controlling a throttle valve provided in a vehicle engine has also been proposed, as disclosed in, for example, the Japanese patent application published before examination under publication number 59/10750. In such a throttle valve control system, an accelerator position sensor, for detecting a controlled change in the position of an accelerator, and an electric actuator, for controlling electrically the throttle valve to have an opening degree corresponding to the controlled change detected by the accelerator position sensor, are provided. The opening degree of the throttle valve is controlled in accordance with a predetermined relation between the opening degree of the throttle valve and the controlled change in position of the accelerator. With the throttle valve control system thus proposed previously, it is possible to have a throttle valve operation that is optimal for a condition or state of travel of a vehicle employing the system, for example, by reducing a rate of variation in the opening degree of the throttle valve to the operated rate of change in the position of the accelerator when the vehicle is travelling on a rough road.
In the vehicle to which such a throttle valve control system, as described above, is applied, it is desired, for obtaining superior acceleration at the starting of the vehicle or in an accelerating condition wherein the vehicle is accelerated from an intermediate travelling speed, to increase the rate of variation in the opening degree of the throttle valve to the operated rate of change in position of the accelerator, so that the response of the acceleration of the vehicle engine is improved. However, in the case where the rate of variation in the opening degree of the throttle valve to the controlled rate of change in position of the accelerator is increased in a range of relatively small operated rate of change in position of the accelerator for the purpose of improving acceleration at the starting of the vehicle, the operability of the vehicle engine is deteriorated when the vehicle is travelling in a traffic jam condition. That is, if the rate of variation in the opening degree of the throttle valve to the operated rate of change in position of the accelerator is set to be relatively large when the vehicle is travelling in the traffic jam condition, then the travelling speed of the vehicle will be varied quickly in response to even a slight controlled change in the position of the accelerator. Therefore, it is necessary that the accelerator be subjected to a careful and delicate control by a driver of the vehicle. Such a careful and delicate control of the accelerator by the driver of the vehicle results in a problem whereby the driver of the vehicle becomes increasingly stressed and fatigued when the vehicle is travelling in a traffic jam condition.